The present invention relates to a synchronous machine drive apparatus fed by a static power converter consisting of solid state switches.
A commutatorless motor is well known as one of this kind of apparatus. A typical prior art example of this kind of apparatus is shown in FIG. 1 which comprises a combination of a three-phase synchronous machine and a converter with a three-phase AC output. The three-phase synchronous machine is provided with a stator having AC windings (armature windings) 101 to 103 and a DC excited rotor 200. The three-phase AC output converter 300' may be an inverter or a cycloconverter, and the inverter is depicted in the figure. As is known, the synchronous machine drive apparatus uses a direct axis field winding (first exciting winding having a first axis) 210 and a compensating winding (second exciting winding having a second axis) 220 both being disposed around the DC excited rotor 200, in order to neutralize the armature reaction of the synchronous machine (see, for example, U.S. Pat. No. 3,749,991, herewith incorporated by reference).
Let us consider now the operation of the conventional apparatus. When a positive half wave i.sub.wp of a W-phase is commutated to a positive half wave i.sub.up of a U-phase, i.e. in a solid state switch 3.sub.wp conduction is completed and current is shifted to a solid state switch 3.sub.up, conductors in which armature current changes due to the commutation are distributed over conductors belonging to the U- and W-phases (in FIG. 1, space distributions of the conductors are shown by black coated belts). The conductors are distributed in slots within a space corresponding to an electrical angle .theta..sub.u ranging from 2/3.pi. (in the case of a Y-connection) to .pi.(in the case of a .DELTA.-connection). When the commutation is finished, the distribution range of armature currents of one polarity becomes the distribution range of the conductors belonging to the U- and V-phases, this distribution range expressed by a space corresponding to an electrical angle .theta..sub.load ranging from (2/3).pi. to .pi.. As shown in FIG. 1, the synchronous machine is connected with a Y-connection so that .theta..sub.u =.theta..sub.load =(2/3).pi.. In the case of a .DELTA.-connection, both are .pi..
As shown in FIG. 1, the compensating winding 220 does not coincidently correspond to the distribution range of the above-mentioned armature current. The reason for this is that the distribution range of the compensating winding 220 is narrow or the relative positions of these windings confronting each other across the gap are displaced with respect to each other due to the power factor angle .phi.. For this reason, it is difficult to correctly compensate the armature reaction due to the distribution of the armature currents.
The distribution range .theta..sub.u of the commutating windings coincidently corresponds to that of the quadrature axis magnetic flux with respect to the surfaces facing through the gap. Particularly, in the case of the convex pole, only a part of the magnetic flux of the direct axis convex surface is subject to interlinkage.
Therefore, it has been difficult to secure stability of motor running insuring a constant power factor, stability of commutation, or stability of phase of the armature current fed thereto. Accordingly, it has been impossible to efficiently use the synchronous motor and the static power converter in operating condition in which the static power converter and synchronous machine can achieve safe, stable and high performance.